1. Field of the Invention
The present invention relates to a mattress used for a nursing care bed and the like.
2. Description of the Related Art
In a part of a bed for supporting the human body, a mattress with a cushion function has been used to improve the comfort of sleeping by elastically supporting the human body. This type of mattress is made of elastic materials such as urethane foam, for example.
When a user, who has disabled from himself or herself from turning over in bed, continues to use a conventional mattress for a long period of time, reaction forces against the body pressure (due to the body weight) are exerted continuously on the user's body part, thus posing a risk of developing bedsores caused by interrupted blood circulation and the like. Therefore, in order to prevent bedsores from developing, a movable mattress is proposed that can distribute the reaction forces substantially applied against the body pressure of the user, by means of changing the working points of the user's body pressure through the use of fluid pressure.
This movable mattress has its working portion of the body pressure (that supports the human body) composed of multiple cells arranged in rows and columns, wherein the cell heights are set to vary at a predetermined timing by means of drawing fluid such as outside air into a fluid chamber and exhausting it therefrom to adjust the inner pressure of the cells. This causes the cells that substantially support the user's body and those that do not to interchange with each other at a predetermined timing, thus preventing the user's body parts from being compressed for a long time due to the body pressure. Also, properly controlling the cell height at each location makes it possible to bring the surface of the mattress in line with the body contour and to promote distribution of body pressure, thus enabling to prevent concentration of loads from working on the bulging parts of the user's body (e.g. buttocks). Such mattress is described, for example, in Publication of Japanese Patent No. JP-B-2615206.
However, in a structure where fluid such as outside air is drawn and exhausted to and from the fluid chamber of each cell to adjust the cell height, the width dimension of each cell in the direction of alignment is naturally reduced as each cell is inflated by air supplied thereto. Therefore, as indicated in JP-B-2615206, a gap is formed between each pair of cells under an inflated condition thereof, which reduces the surface area that supports the user's body, posing a risk of not getting enough distribution of body pressure. Also, a larger gap between each pair of cells sometimes causes each cell to tilt more than necessary to fail to position itself at a desired height position. As a result, the surface configuration of the mattress cannot be aligned properly to follow the body contour, posing a risk of generating a local pressure to cause discomfort for the user.